A-scan ultrasound has been used in ophthalmology to analyze eye tissue and/or structures for over half a century. As is well known in the art, an A-scan ultrasound device merely provides one-dimensional information relating to the scanned structure, e.g., length of an eye. Thus, its application was and remains limited.
To overcome the drawbacks associated with A-scan devices, B-scan devices were developed. As is well known in the art, a typical B-scan device provides two-dimensional (2D) information relating to the scanned structure. A B-scan device can thus provide a sectional image of the retina and other eye structures, and facilitate assessments of vitro-retinal relationships more precisely.
As is also well known in the art, earlier B-scan devices typically employed an ultrasonic frequency in the range of 8-10 MHz. Although the resolution of 10 MHz B-scan devices is sufficient to explore the retina as a whole, it does not provide sufficient resolution of anterior segments or regions.
Furthermore, in order to perform an examination of an anterior segment at 10 MHz, it is necessary to implement immersion with appropriate cupules so as to bring the focal zone which is situated at 23 mm onto the anterior segment.
More recently, B-scan devices employing an ultrasonic frequency of 50 MHz were developed. A commercial version of a high frequency B-scan device is the Ultrasound BioMicroscope (UBM) device distributed by Humphrey-Zeiss. A further device is disclosed in U.S. Pat. No. 5,369,454.
Use of the high frequency UBM device facilitated exacting analyses of anterior segments and adjacent areas of the eye. For example, in 1994, Boker, et al. published a study of the sclerotomy site after pars plana vitrectomy (T. Boker, M. Spitznas, Ultrasound Biomicroscopy for Examination of the Sclerotomy Site After Pars Plana Vitrectomy, American Journal of Ophthalmology, vol. 15, pp. 813-815 (1994). In 1995, Azzolini, et al. reported imaging the presence of intra-vitreous silicone residue in the anterior portion of the vitreous cavity (C. Azzolini, L. Pierro, M. Condenotti, F. Bandello, R. Brancato, Ultrasound Biomicroscopy Following the Intraocular Use Of Silicone Oil, International Ophthalmology, vol. 19(3), pp. 191-195 (1995).
In 1996, Zografos, et al. published a UBM study of 55 cases of uvea melanomas situated in contact with or close to the ciliary body (L. Zografos, L. Chamot, L. Bercher, Contribution of Ultrasound Biomicroscopy to Conservative Treatment of Anterior Uveal Melanoma, Klin. Monast. Augen, vol. 208(5), pp. 414-417 (1996). The conclusion of that work did, however, show that the high attenuation of the high frequency ultrasound signal limits the use of a UBM to structures situated in the direct vicinity of the wall of the eye. Nevertheless, the contribution of high frequency signals in monitoring uvea melanomas after conservative treatment was seen to be considerable.
Further, in 1997, Minamoto, et al. employed a high frequency UBM device to study the separation of the ciliary body situated at the junction between the anterior segment and the posterior segment in the event of hypotony after vitrectomy (A. Minamoto, K. E. Nakano, S. Tanimoto, Ultrasound Biomicroscopy in the Diagnosis of Persistent Hypotony After Vitrectomy, American Journal of Ophthalmology, vol. 123(5), pp. 711-713 (1997).
There are, however, several drawbacks and disadvantages associated with high frequency B-scan devices. A major drawback associated with high frequency B-scan devices is that they are typically limited to two-dimensional imaging of scanned structures. As is well known in the art, two-dimensional images are not very precise.
A further major disadvantage associated with high frequency B-scan devices is that little, if any, information can be obtained at the focal point of the transmitted therapeutic beam. Thus, the location of a focused beam and its thermal effect on the target structure or tissue cannot be observed in real-time. Real-time information on the status of the tissue response or the thermal effect, such as coagulation or tissue contraction of the deep structures, therefore cannot be obtained.
Further, peripheral lesions are difficult to image and diagnose. Moreover, even if a lesion, e.g. a tumor, is diagnosed, its dimensions must be calculated indirectly and separately.
Volumetric information relating to scanned structures also cannot be obtained with high frequency B-scan devices. Since volumetric information is not possible, imaging of the treated area and actual treatment must be done sequentially.
In view of the aforementioned drawbacks associated with B-scan devices, there have been efforts to develop improved B-scan devices and methods that provide three-dimensional images of scanned structures. Illustrative is the high frequency B-scan device and method disclosed in U.S. Pat. No. 5,369,454.
The device disclosed in U.S. Pat. No. 5,369,454 includes an ultrasound transducer that is mounted on a pair of linear positioners that are at right angles to each other. The use of two linear positioners allows data to be obtained in sequential, parallel scan planes from which three dimensional images are constructed.
Prior to subjecting a patient's eye to an ultrasound scan, a light source is positioned above a liquid bath in which the patient's eye is submerged. A beam of alignment light is directed at the submerged eye and another light source is positioned above the patient's second eye. The second light source is then moved until the patient indicates a fusion of the light sources into a single spot, at which point it is known that the visual axes of the eyes are vertical and aligned.
During scanning, radio frequency echo data are digitized at a high rate (i.e. well above the Nyquist rate) and images are constructed from the stored radio frequency data.
There are several drawbacks and disadvantages associated with the noted B-scan device. A major drawback is that the eye is scanned with a single beam via linear translation of the transducer. The curved specular surfaces of the eye, especially the cornea, thus result in significant signal loss as the angle of the surface departs from the normal to the transducer axis. For this reason, data acquired by linear scanning are typically limited to an area of 3-3.5 mm in diameter of cornea and images of the anterior segment to one quadrant at a time.
Further, during scanning with the B-scan device, as well as most known conventional B-scan devices, the eye is open and the cornea and conjunctiva are exposed to methycellulose and the moving ultrasonic transducer or probe. B-scan devices thus cannot guarantee a sterile field.
The noted B-scan device, and devices similar thereto, have thus not been found useful for clinical routine three dimensional images and/or representations of ocular structures.
It would thus be desirable to provide apparatus, systems and methods for providing rapid, accurate representations of biological structures; particularly eye structures.
It is therefore an object of the present invention to provide apparatus, systems and methods for providing rapid, accurate representations of biological structures; particularly eye structures.
It is another object of the present invention to provide ultrasonic scanning apparatus, systems and methods for providing rapid and accurate three-dimensional (3-D) images of scanned biological structures and/or tissue associated therewith.
It is another object of the present invention to provide ultrasonic scanning apparatus, systems and methods for providing rapid and accurate three-dimensional (3-D) images of scanned biological structures during therapeutic procedures.
It is another object of the present invention to provide ultrasonic scanning apparatus, systems and methods for providing rapid and accurate three-dimensional (3-D) images of scanned biological structures and the focal point of the transmitted therapeutic energy (i.e. beam) during therapeutic procedures.